1. Field of the Invention
The invention is in the field of iontophoresis. In particular, the invention relates to an iontophoretic drug delivery system, having an iontophoretic controller and patch, which automatically detects when certain events or conditions occur in the system. Such events or conditions may include the substantial depletion of the conductive material of the electrodes of the iontophoretic patch or failure of the iontophoretic controller. In response to the detection of an event or condition, such as, for example, a fault, the system performs an action such as providing a warning or stopping the supply of iontophoretic current to the iontophoretic patch.
2. Description of Related Art
Iontophoresis is the application of an electrical current to transport ions through intact skin; the ionized species are usually the ionic form of a drug or other therapeutic agent. One particularly advantageous application of iontophoresis is the non-invasive transdermal delivery of ionized drugs into a patient. This is done by applying current to the electrodes of the iontophoretic patch. The electrodes are respectively arranged within a drug reservoir, containing the drug ions, and a return reservoir, containing an electrolyte. When the patch is placed on skin of a patient, current applied from the iontophoretic current controller forces the ionized drug contained in the drug reservoir through the skin and into the patient. Iontophoretic drug delivery offers an alternative and effective method of drug delivery to other drug delivery methods such as passive transdermal patches, needle injection, and oral ingestion, and is an especially effective method for children, the bedridden and the elderly.
Typically, during iontophoresis, as a constant, controlled current is applied through the patch (current-time curve, FIG. 1A, portion B), the voltage across the patch monotonically decreases as a function of time (voltage-time curve, FIG. 1B, portion B) due to decreasing skin impedance during the process (resistance-time curve, FIG. 1C, portion B). (The initial increase in voltage, portion A of FIG. 1B, is a transient state caused by turning on the patch, as will be explained in more detail below.) There may also be occasional small amplitude, short duration, increases or decreases in the voltage due to patient or patch movement or due to electrical noise (not shown).
However, certain conditions can cause a relatively larger amplitude, longer duration, change (up-ramping or down-ramping) of the voltage. These conditions include, but are not necessarily limited to: poor contact between the patch and skin, the patch being substantially depleted of drug or other ions, the patch being substantially depleted of electrode material, certain failures of the iontophoretic current controller, an improper electro-chemical reaction, damage to the patch or contacts, and excessive electrical noise from some external source. Moreover, a patient may attempt to reuse a patch having a substantially depleted electrode or drug reservoir, which would also cause an undesirable large amplitude, long duration, voltage increase.
All of these conditions may interfere with the safe and effective iontophoretic delivery of the drug to the patient. Moreover, when the voltage suddenly changes, the patient may feel an uncomfortable sensation at or near where the patch is attached.